Tires: General Truths, Misconceptions, & Subjective Opinions

Tire choices are a hotly contested issue, and there are quite a few generally held “truths” out there—some of which bear more basis in reality than others.

So this week, three of our reviewers weigh in on some of the more commonly held beliefs regarding rubber.

Of course, there’s no such thing as the definitive word in tire choice, but when you’re shopping for a new set of shoes for your ride, we hope this discussion might provide a little food for thought.

TRUISM #1: Higher volume tires provide a smoother ride.

NOAH BODMAN: Generally true, but obviously there’s more to it than that. Tire pressure makes a massive difference, and differences in tire casings are certainly noticeable as well. But all other things being equal, a higher volume tire is more comfy than a low volume one.

Blister Gear Review Topic of the Week - Mountain Bike Tires
Noah Bodman, Whistler, BC.

MARSHAL OLSON: A bigger tire at the same pressure as a narrower tire of the same weight will provide less feedback to the rider, because the casing is flexing more (the wall of the bigger tire is thinner). That is bad, not good.

There are a lot of ways to tune a bike’s ride: rim choice, spoke choice, suspension setup, frame materials and design, wheel size, tire casing, etc.

TOM COLLIER: At a given air pressure, a higher volume tire has more ability to displace as you roll over roots. That is good news, as it (1) can provide more grip by better conforming to the terrain, and (2) it can take the edge off bumps. This second part doesn’t matter too much on a full suspension bike, but it is nice on a hardtail.

The bad news is that this motion is un-damped and uncontrolled, and it doesn’t just flex up and down, it flexes sideways as well. This can make performance unpredictable if the tire flexes through turns. So it isn’t a full substitute for suspension. Like anything else, it is a balance.

A tire with too little volume at a reasonable pressure for traction is going to bottom out easily on rocks and roots, resulting in rim strikes. But a tire with too much volume can squirm. Tire casing stiffness matters, air pressure matters, rim width matters. None of these things are simple.

Marshal: Just my opinion, but high quality suspension with clean break-away will allow the bike to track over roots/rocks, but not sacrifice the way a big soft tire does in every other scenario.

Noah: This point ^^^ bears repeating. There’s a big trend toward massive tires these days. Big tires might provide a smooth ride, but like Tom said, it’s undamped and uncontrolled.

Engineers and garage tinkerers have spent the last 60 years or so dialing in suspension to maximize traction in variable scenarios. Strapping giant balloons to your rims might be comfy, but it’s not the same thing by a long shot.

TRUISM #2: More, smaller knobs provide better grip on hardpack.

Marshal: No, not at all. 100% disagree.

Small knobs roll faster on hardpack, because they create less friction and therefore have less grip than knobby tires. The point is that you don’t need a ton of grip on hardpack since the surface is inherently grippy (ie. sandpaper).

Tom: Shorter knobs are better on hard surfaces because they generally squirm less and provide more contact area. If you imagine running a spike tire on pavement it would feel awful because the knobs aren’t able to sink in and you would only ride on the small area at the top of each spike.

Noah: Generally speaking, sort of. Big knobs work well when they sink into the dirt, but all they do is squirm around when they can’t sink in. So when dirt is really hardpacked, small knobs squirm less. The more important thing on hardpack is that the knobs are spaced more closely together, effectively making the tire a bit smoother. That means more non-squirmy rubber on the ground, which means more traction. As soon as the dirt gets a little bit soft though, traction takes a dive.

TRUISM #3: More open space between knobs yields better mud clearing abilities and better traction in soft soil.

Noah: As to the mud clearing – yeah, pretty much. There’s some other stuff that factors into a tires mud clearing abilities (knob shape being important), but knob spacing is definitely factor #1.

As for better traction in loose soil, I’d say… sort of. Yes, spaced-out knobs mean that each individual knob can dig into the soil and do its thing. But knob shape, knob height, and knob placement have a huuuge effect on this. A tire with low, poorly placed knobs, even if they’re spaced out, is going to get horrible traction compared to a more tightly packed tire with the knobs in intelligent places.

Another really important factor to keep in mind is that “traction” is really a generalization. A tire is really asked to do 3 things: (1) move the bike forward, (2) slow the bike down, and (3) make the bike go around corners. It’s easy to get caught up in the cornering part of the discussion, but climbing and braking matter too. And for each aspect of traction, the ideal knob placement and shape isn’t necessarily the same. Just because a tire grips like hell in a loose corner doesn’t mean it’s going to climb or brake well.

Marshal: Tread patterns that are more open = better clearing of mud.

Loose soil traction is more about knob depth and knob and tire surface area than knob spacing. A tire that is too big floats and surfs (bad). Narrower tires with pointy knobs can dig in there and grip. Knob height is also important because the face of the knob dictates traction for pedaling and braking traction, rather than the top surface.

Tom: There is definitely more to it than just spacing, and any tire designer needs to know how to design knobs that are sufficiently tall and shaped well enough to provide grip in mud or soft soil. However, this is less critical for riders to worry about. It is pretty rare to find a tire that has widely spaced and short knobs—unless it formerly had tall knobs and they wore down.

I agree with Noah and Marshal that knob spacing is the critical factor for determining how well a tire clears mud. Traction is definitely a more complex issue…

Marshal makes a good point about knob height being critical for braking and pedaling traction. I’d go a bit further, though, and blend in Noah’s point that traction is critical for 3 different activities. All knobs play a role in braking and pedaling traction, but the center knobs are most critical.

We’ve all been told that we are supposed to avoid braking in corners. In theory, that means your bike is usually upright when you hit the brakes

When you are worried about pedaling traction, you are usually going slowly, and at low speeds bikes are usually pretty upright.

When a tire is upright, the center knobs are most prominent, and provide most of the contact with the trail. Therefore, center knob shape is critical to braking and pedaling traction.

Squarer and taller knobs provide more grip. Ramped knobs provide less grip, but therefore they can also role more quickly.

For corners, the same principles of knob shape apply, but the load is primarily on the outside knobs and the forces are at ninety degrees to braking and pedaling forces.

An interesting side point is knob siping. Sipes are thin cuts through knobs.

Blister Gear Review Topic of the Week - Tires
Siped Knobs vs. Un-siped Knobs

They add more sharp edges to provide traction, and allow knobs to better conform to terrain—again for more traction. However, they let knobs flex and squirm a bit more and can increase tire wear rate.

NEXT: Tire Pressure, Soft vs. Hard Compounds, & the Tires our Reviewers Typically Run

9 comments on “Tires: General Truths, Misconceptions, & Subjective Opinions”

  1. Nice write up, I like the mixing of opinions. I’m a bit of a tire nerd, so I’ll throw a bit into the mix.

    TRUISM #2: More, smaller knobs provide better grip on hardpack.
    The more rubber you can get on the hardpack at one time the better. Smaller knobbed tires are usually combined with density. Foldy knobs on hardpack feel inconsistent and therefor untrustworthy. Loose over hard and you will want the smaller knobs for trapping the loose dirt for better grip.

    TRUISM #4: Smaller tires with higher pressure roll faster.
    Higher pressure just bounces you around and you FEEL faster due to all the feedback you receive. A conforming tire (lower pressure) can pass through smaller obstacles or minimize them keeping energy moving forward rather than the energy bouncing up.

    Also a comment on rolling resistance. RR is primarily a function of rubber compound, and it’s rebound characteristics, with knob design much further down in importance. For example, a Nobby Nic is a wide pattern fast roller, while an Ardent has a condensed center but is a not fast roller. The difference is the rubber compound in the casing. After the casing flexes down, it gives back energy in rebound, Nobby Nic is a high rebound rubber casing, the Ardent is the moderate rebound 60a in the casing. Or really I should just point out the Hans Dampf, PaceStar = fast, TrailStar = moderate, VertStar would be sloooow. I’ve had big knobbed tires roll fast, and small knobbed tires roll slow (Small Block 8). There are measured tests that bear this out. German Bike Magazine used to do testing on RR. IMHO, RR trumps weight for energy savings.

    The other bit of nerdiness I learned, is to think about a tire pattern in negative space or the open space between knobs, as that is where the loose dirt is trapped, and it is the trapped dirt that creates the real friction or grip, more so than the knob. I picked that one up from a tire designer on a forum. It took me a while to get my head around that one.

    One last bit, I believe it helps to judge a tire pattern when it is flat (rather than inflated and rounded on top of a wheel) the reason is that at the tire-to-ground-contact, the tire is (basically) flat and not rounded off.

    Sorry for rambling. I am a reformed tire addict.

    …I guess not so reformed.

    • Mr. P,

      Great input. Your points about rubber compounds and looking at negative space between knobs ring true for me. I’m not with you on smaller, tightly packed knobs for loose over hard though – unless there is only a thin layer of loose material. I have had the best luck in those scenarios with fewer, taller, more spread out knobs that leave plenty of space for the loose material to filter between them, and allow the knobs to penetrate down to the hard trail surface.

  2. Marshall: briefly, how does the Butcher 2.3 compare to a Minion DHF 2.5 for performance, durability, tubeless reliability etc?

    I’ve been on DHF/DHR2 EXOs front & back on my trail bike for the past few years, trying some Schwalbe options to start this summer but I was curious about Butchers too.

    • I can jump in on that one – I had good luck with the Butchers. I ran one with a lighter weight casing (can’t remember which one exactly) on the front of my Enduro, and I had the DH casing Butchers on my Demo for a while. In both situations, they wore at roughly the same rate as a DHF, and the casings seemed comparable to the equivalent from Maxxis (i.e. the DH casings from both companies were similar). Traction in all regards was very similar between the two tires. Theoretically, the DHFs might handle leaned over braking slightly better due to a more pronounced pocket on every other sideknob, but in reality, I’m not sure I could tell a difference. All in all, I wouldn’t hesitate to run the Butchers as a DHF alternative.

  3. These round table articles are always a good read. Thanks.
    More and more, I feel like the tire discussions of the MTB world perpetrate this idea that riders are like a sommelier describing the nuances in $500 bottles of wine, constantly swishing and spitting from one to the other for the love of the “science”. The thought that we’re all constantly flipping tires runs in stark contrast with the hassle most of us admit to being the reality of setting up tubeless tires. Unless I had duplicate wheelsets, I can’t imagine doing a bunch of side by sides. I appreciate you guys’ candor in suggesting that you tend to pick a tire and stick to it until it’s been destroyed. Which means that in most cases tire comparisons are very unscientific, as they’re more the result of retrospectively trying to compare how things went last fall with how they’re going this spring, perhaps on a different bike or rim or trail. For myself, I tend to buy whatever rubber my internet friends and my outernet friends (real life people) are pimping. Eventually I either love them because they hold up well, or I pull them because they tear or wear down too easily. If I think they served me well I get them again, otherwise I try something new and sexy. Then the retirees spend the rest of their lives in my garage hanging on the used but not quite dead tire chandelier. More and more, as a 26er practitioner I find that I’m choosing from the shrinking pool that is still available for purchase in this forsaken size.

    • Yup – tire reviews, moreso than a lot of other types of reviews, are tricky just because going and back and forth between a couple of options is a huge hassle and the differences between tires can often be pretty subtle. I’ve found demo days can be really good for this (and for comparing a ton of other stuff). Lots of different bikes with lots of different parts, all in one spot, that can be efficiently compared on the same trail in the same conditions.

      But yeah, I think a lot of us just find what we like and stick with it. If it ain’t broke…

  4. With respect to tire comparisons, I’ve found it can be revealing to ride with friends of known skill levels each with different sets of tires. You can get a good feeling of which tire is handling which conditions better; hard, soft, wet, loose, by how your buddy is struggling or pulling away with ease. I wouldn’t draw conclusions after one ride, but after 6 or 12 you can really start to notice where each tire excels or flails.

    I too am too lazy to change my tires, but I do try to remember what everyone was riding and how they handled.

    • Fraser,

      I like your thoughtful approach. One of the most valuable experiences I’ve had was on our testing trip to Whistler last summer. We were frequently able to ride the same descent multiple times, swapping bikes (with different tires) each time. It was great to get that A/B testing in and get multiple opinions on the same tires as well as watching each rider on each set of tires. The differences became clear pretty quickly!

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